This invention relates to melt spinning of particulate polymeric material and more particularly it relates to apparatus for providing a positive hold-up time for the melting material descending from the melt grid to the melt pump beneath the grid.
In the process for producing filaments and fibers from polymeric material as described by Pierce in U.S. Pat. No. 2,683,073, polymer is melted in a melting unit and then flows into a reservoir where it is mixed by a driven stirrer. A pump meters a supply of molten polymer from the reservoir to the spinning orifices. Flores has described in U.S. Pat. No. 2,916,262 construction and use of a heated grid for melting the polymer which comprises a double-walled jacket of rectangular plan having a plurality of hollow fin-like elements oriented on longitudinal axes substantially parallel to one another. Heating fluid circulates through the jacket and the fins. When using the Flores grid to provide molten polymer for spinning, polymer flakes are charged into the grid to be melted. During the melting operation it is found that some of the flake is not completely melted. The existence of such unmelted flake creates a problem of spherulite seeding in the extruded fiber. Higher grid unit temperatures have been employed as one solution to the problem to seek complete flake melting to reduce the spherulite problem.